This invention relates to apparatus for cutting off sections of helically formed pipe while the pipe is "on the fly" in the course of manufacture. Apparatus of this general type is known which employs a carriage that supports a cut-off mechanism or torch, the carriage and torch being advanced parallel to the axis of the pipe as the manufactured portion is advanced axially and rotationally. A knife wheel or contact mounted to the carriage engages the pipe and advances the carriage with the pipe. Thus, the cut-off mechanism is also advanced with the pipe, and one complete rotation of the pipe is usually sufficient to completely sever the leading pipe section from a trailing portion. An apparatus of this kind is shown and described in U.S. Pat. No. 3,747,446.